You'll get used to being clipped in over challenging terrain. And of course, you can unclip and and still have your feet on the eggbeaters pedaling.
As far as riding with regular shoes on clipless pedals goes... I don't ever do it because it's hard to pedal this way!
I always switch out my pedals to platforms if I ever need to get somewhere where I'd need regular shoes.
If you don't want to switch pedals, there is the Crank Bros Mallet C pedal. It can be used with or without clipless shoes. However, it is fairly expensive compared to what you've already linked.
http://www.performancebike.com/shop/...tegory_ID=5240